How Long Will My Money Last Calculator (With Worked Examples)
If you have a retirement nest egg, an emergency fund, or a lump-sum payout sitting in an account, the most urgent question is simple: how long will this money actually last? The answer depends on three numbers — your starting balance, how much you pull out each month, and what your money earns while it sits there. This page gives you a working calculator, the real math behind it, and three fully worked examples so you can trust every result.
What you’ll learn on this page:
- 📐 The exact formula used to calculate portfolio longevity
- 🧮 How to use the interactive calculator in four steps
- 📊 Three fully worked examples with step-by-step math
- ⚠️ The most common mistake people make when estimating their runway
- 📋 How the 4% rule compares to a custom withdrawal rate
💡 Quick Answer: To find how long your money will last, use the present-value annuity formula: n = −ln(1 − (r × PV) / PMT) / ln(1 + r), where r is the monthly rate, PV is your balance, and PMT is your monthly withdrawal. If your account earns no interest, it is simply PV ÷ PMT months. A $400,000 balance withdrawn at $2,000/month at 5% annual return lasts about 27 years.
⚡ TL;DR
- 💰 Your money’s lifespan depends on balance, withdrawal amount, and return rate.
- 📉 Even a 1% higher return can add 3–5 years to your runway.
- 🧮 The calculator uses the annuity present-value formula — not a simple division.
- ⚠️ Inflation silently shrinks your real purchasing power every year.
- 📊 The 4% rule is a useful benchmark but not a guarantee for every situation.
📋 Table of contents
💻 How long will my money last? — Calculator
Money Longevity Calculator
Find out how many years your savings will last
% / yr
📐 Step-by-step solution
How to use this calculator
- Enter your balance — the total amount currently in your savings, IRA, 401(k), or investment account.
- Enter your monthly withdrawal — the dollar amount you plan to take out each month (include Social Security or pension income as a reduction here if you want a net figure).
- Enter your expected annual return — use a conservative estimate. A diversified US stock/bond portfolio has historically returned 4–7% after fees. Use 0% for a savings account or cash.
- Click Calculate — the result shows years and months remaining, plus a full step-by-step breakdown.
Switch to “Max monthly withdrawal” mode if you want to work backwards: enter your balance, how many years you need it to last, and the expected return, and the calculator tells you the maximum safe monthly withdrawal.
The formula: how does the math work?
The calculator uses the present-value annuity formula, which is the same equation banks use to calculate loan payoff timelines — just run in reverse. According to the Investopedia — Present Value of an Annuity definition, an annuity is a series of equal payments at regular intervals, and the formula solves for how many periods those payments can continue.
Longevity formula (solving for n):
n = −ln(1 − (r × PV) / PMT) / ln(1 + r)
Where: r = monthly rate (annual % ÷ 12 ÷ 100) | PV = current balance | PMT = monthly withdrawal | n = number of months
If r = 0: n = PV ÷ PMT (simple division)
Variables & symbols table
| Symbol | Meaning | Unit / Notes |
|---|---|---|
| PV | Present value — your starting balance | US dollars ($) |
| PMT | Payment — your monthly withdrawal | US dollars per month |
| r | Monthly interest rate | Decimal (annual rate ÷ 12 ÷ 100) |
| n | Number of periods (months) | Divide by 12 for years |
| ln | Natural logarithm | Built into every calculator/spreadsheet |
PV and PMT must be in the same currency unit (US dollars). The rate r is dimensionless. The result n is in months — divide by 12 for years. If you use an annual withdrawal instead of monthly, use the annual rate directly and divide n by 1 (n = years directly).
Worked examples
Example 1 — The retiree with a 5% portfolio
Inputs: Balance = $400,000 | Monthly withdrawal = $2,000 | Annual return = 5%
Monthly rate r = 5 ÷ 12 ÷ 100 = 0.004167. Fraction = (0.004167 × 400,000) / 2,000 = 1,666.67 / 2,000 = 0.8333. n = −ln(1 − 0.8333) / ln(1.004167) = −ln(0.1667) / ln(1.004167) = 1.7918 / 0.004158 = 430.9 months ≈ 35 years 11 months.
Example 2 — Cash savings, no return
Inputs: Balance = $120,000 | Monthly withdrawal = $1,500 | Annual return = 0%
r = 0, so n = 120,000 ÷ 1,500 = 80 months = 6 years 8 months. This is a common scenario for someone living off a CD or high-yield savings account with a low yield that barely keeps pace with fees.
Example 3 — Max withdrawal mode
Inputs: Balance = $600,000 | Desired duration = 30 years | Annual return = 6%
r = 6 ÷ 12 ÷ 100 = 0.005. n = 360 months. PMT = (0.005 × 600,000) / (1 − (1.005)^−360) = 3,000 / (1 − 0.1660) = 3,000 / 0.8340 = $3,597/month. That is a 7.19% annual withdrawal rate — higher than the 4% rule, but sustainable over exactly 30 years at 6% return.
Portfolio balance over time — $400,000 at 5% return, $2,000/month withdrawal
$400,000 |█████████████████████████████████████
$350,000 |████████████████████████████████
$300,000 |████████████████████████████
$250,000 |████████████████████████
$200,000 |████████████████████
$150,000 |████████████████
$100,000 |████████████
$50,000 |████████
$0 |────────────────────────────────────────
Yr 0 Yr 5 Yr 10 Yr 15 Yr 20 Yr 36
↑ depleted
Withdrawal rate comparison: how long does $500,000 last?
This table shows how the same $500,000 balance lasts under different monthly withdrawal amounts and return rates — a direct answer to the most common question I get from readers.
| Monthly withdrawal | Annual rate = 0% | Annual rate = 4% | Annual rate = 6% | Annual rate = 8% |
|---|---|---|---|---|
| $1,500/mo | 27 yr 9 mo | Never (return > withdrawal) | Never | Never |
| $2,000/mo | 20 yr 10 mo | 41 yr 4 mo | Never | Never |
| $2,500/mo | 16 yr 8 mo | 25 yr 5 mo | Never | Never |
| $3,000/mo | 13 yr 11 mo | 18 yr 2 mo | 27 yr 9 mo | Never |
| $4,000/mo | 10 yr 5 mo | 12 yr 6 mo | 15 yr 8 mo | 22 yr 11 mo |
| $5,000/mo | 8 yr 4 mo | 9 yr 7 mo | 11 yr 3 mo | 14 yr 5 mo |
Note: “Never” means the monthly return on the balance equals or exceeds the withdrawal — the money grows indefinitely. These figures assume a fixed nominal withdrawal with no inflation adjustment.
Common mistakes that shrink your runway faster than you expect
Mistake 1 — Using a gross return instead of a net-of-fees return
A mutual fund that advertises 8% may charge a 1% expense ratio, leaving you with 7% net. Over 25 years on a $500,000 portfolio, that 1% difference costs you roughly $180,000 in lost growth. Always use your after-fee return in the calculator.
Mistake 2 — Ignoring taxes on withdrawals
If your money is in a traditional 401(k) or traditional IRA, every dollar you withdraw is taxed as ordinary income by the IRS. A $3,000 gross withdrawal might net only $2,400 after a 20% effective tax rate. Enter your after-tax withdrawal need, not your gross target.
⚠️ Required Minimum Distributions (RMDs): The IRS requires you to start withdrawing from traditional IRAs and 401(k)s at age 73 (as of the SECURE 2.0 Act). If your RMD exceeds your planned withdrawal, your actual depletion rate will be higher than this calculator shows. Check IRS — Retirement Plan RMD FAQs for current rules.
Mistake 3 — Treating a fixed nominal withdrawal as inflation-proof
$2,500/month in 2026 buys far less than $2,500/month in 2046. The US Bureau of Labor Statistics reports that the long-run average CPI inflation rate is around 3% per year. To account for this, subtract your expected inflation rate from your return rate before entering it in the calculator. If you expect 6% returns and 3% inflation, enter 3% as your effective real return.
Sequence-of-returns risk matters more than your average return. Most longevity calculators — including this one — assume a constant annual return. In reality, the order of good and bad years is critical. If your portfolio drops 30% in year one of retirement and you keep withdrawing $3,000/month, you permanently lock in those losses on a smaller base. Research from financial planning literature shows that two retirees with the exact same 30-year average return can have wildly different outcomes depending on whether the bad years come early or late. The practical fix: keep 1–2 years of withdrawals in cash or short-term bonds so you never have to sell equities at a loss to fund living expenses. This strategy — sometimes called a “cash buffer” or “bucket strategy” — is the single most underused tool in retirement planning, and no simple calculator captures it. Use this calculator to find your baseline runway, then build a cash buffer on top of it.